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Chapter 14. The Arthropods: Blueprint for Success. Evolutionary Perspective. Metamerism modified by tagmatization Chitinous exoskeleton Paired, jointed appendages Ecdysis Ventral nervous system Coelom reduced to cavity around gonads Open circulatory system Complete digestive tract - PowerPoint PPT Presentation
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Chapter 14 The Arthropods: Blueprint for Success
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Page 1: Chapter 14

Chapter 14

The Arthropods: Blueprint for Success

Page 2: Chapter 14

Evolutionary Perspective1. Metamerism modified by tagmatization2. Chitinous exoskeleton3. Paired, jointed appendages4. Ecdysis5. Ventral nervous system6. Coelom reduced to cavity around gonads7. Open circulatory system8. Complete digestive tract9. Metamorphosis often present

Page 3: Chapter 14

Classification and Relationships to other Animals

• Ecdysozoans– Cuticle, ecdysis, loss of epidermal cilia

(figure 14.2)• Monophyletic with five subphyla

(table 14.1)– Chelicerata, Crustacea, Hexapoda,

Myriapoda, Trilobitomorpha (entirely extinct)

Page 4: Chapter 14

Figure 14.2 Evolutionary relationships of the arthropods to other animals.

Page 5: Chapter 14

Table 14.1

Page 6: Chapter 14

Metamerism and Tagmatization• Metamerism evident externally– Segmental body wall– Segmental appendages

• Metamerism reduced internally– No septa– Most organs are not metameric

• Tagmatization obvious– Specializations for feeding, sensory

perception, locomotion, and visceral functions

Page 7: Chapter 14

Learning Outcomes: Section 14.3

• Describe the structure of the arthropod exoskeleton or cuticle.

• Assess the influence the exoskeleton has had on the evolution of the arthropods.

Page 8: Chapter 14

The Exoskeleton• Exoskeleton or cuticle– External jointed skeleton

• Functions– Structural support– Protection– Prevents water loss– Levers for muscle attachment and movement

• Covers all body surfaces and invaginations• Secreted by epidermis (hypodermis)

Page 9: Chapter 14

The Exoskeleton• Epicuticle (figure 14.3)

– Lipoprotein– Impermeable to water– Barrier to microorganisms and pesticides

• Procuticle– Chitin

• polysaccharide– Outer procuticle hardened by sclerotization or deposition of

calcium carbonate– Inner procuticle less hardened and flexible

• Articular membranes at joints (figure 14.4)• Modifications include sensory receptors

– Sensilla

Page 10: Chapter 14

Figure 14.3 Arthropod exoskeleton.

Page 11: Chapter 14

Figure 14.4 Modifications of the exoskeleton.

Page 12: Chapter 14

The Exoskeleton• Growth accompanied by ecdysis (figure

14.5)1. Enzymes from hypodermal glands begin

digesting old procuticle (a, b).2. New procuticle and epicuticle secreted (c,

d).3. Old exoskeleton splits (e)4. Calcium carbonate deposition and/or

sclerotization hardens new exoskeleton (f).

Page 13: Chapter 14

Figure 14.5 Events of ecdysis.

Page 14: Chapter 14

The Hemocoel• Embryonic blastocoel• Internal cavity for open circulatory

system– Fluids bathe internal organs.– Exchange of nutrients, wastes, and

sometimes gases• Not a hydrostatic compartment

Page 15: Chapter 14

Metamorphosis• Radical change in body form and

physiology as an immature (larva) becomes an adult.– Reduces competition between adult and

immature stages

Page 16: Chapter 14

Subphylum Trilobitomorpha• Dominant life form from Cambrian

period (600 mya) to Carboniferous period (345 mya)

• Substrate feeders• Three tagmata: head, thorax, and

pygidium• Three longitudinal sections • Biramous appendages

Page 17: Chapter 14

Figure 14.6 Subphylum Trilobitomorpha (Saukia sp).

Page 18: Chapter 14

Subphylum Chelicerata• Spiders, mites, ticks, horseshoe crabs• Two tagmata

– Prosoma• Eyes• Chelicerae

– Often chelate– Usually feeding appendages

• Pedipalps– Sensory, feeding, locomotion, reproduction

• Walking legs – Opisthosoma

• Digestive, reproductive, excretory, and respiratory organs

Page 19: Chapter 14

Class Meristomata• Subclasses– Eurypterida

• Extinct giant water scorpions

(figure 14.7)

Figure 14.7 A eurypterid, Euripterus remipes.

Page 20: Chapter 14

Class Meristomata– Subclass Xiphosura

• Horseshoe crabs– Limulus (Atlantic

Ocean and Gulf of Mexico)

– Book gills» Gas exchange

between blood and water

– Reproduction» Dioecious» External

fertilization

Figure 14.8a Limulus polyphemus.

Page 21: Chapter 14

Figure 14.8b Ventral view of Limulus.

Page 22: Chapter 14

Class Arachnida• Spiders, mites, ticks, scorpions• Arose from ancient euryptrids• Very early terrestrial groups– 280-400 mya– Exoskeleton was preadaptation for water

conservation.

Page 23: Chapter 14

Form and Function• Carnivores– Chelicerae to hold prey or as fangs– Gut

• Foregut – Cuticular – Pumping stomach

• Hindgut– Cuticular – Water reabsorption

• Midgut– Noncuticular– Secretion and absorption

Page 24: Chapter 14

Form and Function• Excretion– Coxal glands

• Paired sacs bathed in blood of body sinuses• Homologous to nephridia• Excretory pores at base of posterior

appendages– Malpighian tubules

• Blind ending diverticula of gut tract• Empty via digestive tract

– Uric acid

Page 25: Chapter 14

Form and Function• Gas Exchange– Book lungs• Paired ventral invaginations of body wall• Gas exchange between air and blood across

book lung lamellae– Tracheae• Branched, chitin-lined tubes• Open at spiracles along abdomen

Page 26: Chapter 14

Figure 14.9 An arachnid book lung.

Page 27: Chapter 14

Form and Function• Circulation– Open with dorsal contractile vessel– Pumps blood into tissue spaces of

hemocoel– Returns to dorsal vessel via ostia

• Nervous system– Ventral with fusion of ganglia

Page 28: Chapter 14

Form and Function• Senses

– Mechanoreceptors• Modifications of

exoskeleton• Sensilla respond to

displacement.– Chemical sense

• Pores in exoskeleton– Vision

• Eyes detect movement and changes in light intensity.

Figure 14.10 An arthropod seta (a) and an eye (ocellus) (b).

Page 29: Chapter 14

Form and Function• Reproduction– Dioecious– Indirect sperm transfer

• Male deposits spermatophores, which are transferred to the female.

– Courtship rituals common– Copulation occurs in spiders via modified

pedipalp of male.• Development– Direct

Page 30: Chapter 14

Order Scorpionida• Prosoma– Shieldlike carapace

• Opisthosoma– Preabdomen– Postabdomen (“tail” with sting)

• Courtship prior to mating• Oviparous, ovoviviparous, or

viviparous

Page 31: Chapter 14

Figure 14.11 (a) Hardrurus arizonensis (b) External anatomy.

(a)

(b)

Page 32: Chapter 14

Order Araneae• Spiders• Prosoma– Chelicerae with poison glands and fangs– Pedipalps leglike

• Sperm transfer in males– 6-8 eyes

• Opisthosoma– Connected to prosoma via pedicel– Swollen or elongate– Visceral functions and spinnerets

Page 33: Chapter 14

Figure 14.12 External structure of Argiope.

Page 34: Chapter 14

Figure 14.13 Prosoma of a spiderling.

Page 35: Chapter 14

Order Araneae• Silk– Protein– Repeating sequence of glycine and alanine– Beta sheet– Stored as gel prior to spinning– Chemical modification when forced through

spinnerets• Webs, line retreats, safety lines, wrapping

eggs, dispersal of young (ballooning)

Page 36: Chapter 14

Figure 14.14 Members of the family Araneidae are the orb weavers.

Page 37: Chapter 14

Order Araneae• Feeding– Insects and other arthropods– Hunt or capture in webs– Paralyze prey• May wrap in silk

– Inject enzymes into prey body wall• Two spiders are venomous to

humans.

Page 38: Chapter 14

Figure 14.15 (a) Black widow spiders (Lactrodectus mactans) has a neurotoxic venom. (b) Brown recluse spiders (Loxosceles reclusa) have a histolytic venom.

(a)

(b)

Page 39: Chapter 14

Order Araneae• Reproduction– Complex behaviors• Chemical, tactile, and visual signals

–Male’s pedipalps enlarged into embolus• Male deposits sperm on web and collects

with pedipalps.• Transfers sperm to female during mating

– Female deposits eggs in silk case.• In webbing, a retreat, or carries with her

Page 40: Chapter 14

Order Opiliones• Harvestmen or

daddy longlegs• Prosoma broadly

joins opisthosoma• Legs long and

slender• Omnivores• External and

internal digestion

Figure 14.16 Order Opiliones (Leiobunum sp).

Page 41: Chapter 14

Order Acarina• Mites

– Prosoma and opisthosoma fused and covered by single carapace

– 1mm or less– Free-living

• Herbivores or scavengers– Many pest species

– Ectoparasites• Chigger (Trombicula)• Follicle mite (Demodex)

Figure 14.17 Dermatophagoides farinae is common in homes and grain storage areas.

Page 42: Chapter 14

Order Acarina• Ticks– Ectoparasites in all life stages– Up to 3cm– Females lay eggs after engorging with

blood.– Important in disease transmission• Rocky Mountain spotted fever• Lyme disease

Page 43: Chapter 14

Figure 11.18 Ixodes scapularis transmits the bacteria that causes Lyme disease.

Page 44: Chapter 14

Class Pycnogonida (Subphylum Cheliceriformes?)

• Sea spiders• Marine• Feed on cnidarian polyps• Dioecious• Molecular,

developmental, and morphological characters are being used to reevaluate taxonomic status.

Figure 14.19 Class Pycnogonida

Page 45: Chapter 14

Subphylum Crustacea• Crayfish, shrimp, lobsters, crabs,

copepods cladocerans and others• Almost all are aquatic– Terrestrial isopods and crabs are

exceptions.• Two pairs of antennae• Biramous appendages (figure 14.20)

Page 46: Chapter 14

Figure 14.20 Crustacean body form. (a) External anatomy. (b) Biramous appendages.

Page 47: Chapter 14

Class Malacostraca• Crabs, lobsters, crayfish, shrimp,

krill, amphipods, isopods• Order Decapoda– Largest order– Shrimp, crayfish, lobsters, crabs

Page 48: Chapter 14

Class Malacostraca• Crayfish external structure– Cephalothorax

• Fusion of head and thorax• Covered dorsally and laterally by carapace• Sensory, feeding, locomotion

– Abdomen• Muscular “tail” in crayfish• Locomotor and visceral functions in others

– Paired appendages• Serially homologous (derived from a common

ancestral pattern)

Page 49: Chapter 14

Figure 14.22 External structure of a male crayfish.

Page 50: Chapter 14

Figure 14.23 Serial homology of crayfish appendages.

Page 51: Chapter 14

Class Malacostraca• Crayfish internal structure

– Digestive system• Complete with foregut, midgut, and hindgut

– Respiratory system• Gills attach at base of cephalothoracic appendages.• Lie within gill chamber between carapace and lateral body

wall• Second maxilla circulates water.

– Circulation• Open• Dorsal heart and major arteries• Blood enters hemocoel, and gills before returning to

pericardial sinus around heart.

Page 52: Chapter 14

Figure 14.24 Internal structure of a crayfish.

Page 53: Chapter 14

Class Malacostraca• Ventral nervous system

– Cephalization and centralization– Supraesophageal and subesophageal ganglia process

sensory information and control head appendages.– Segmental ganglia

• Sensory structures– Antennae– Compound eyes– Statocysts– Chemoreceptors– Proprioceptors– Tactile setae

Page 54: Chapter 14

Class Malacostraca• Endocrine system– Ecdysis, sex determination, color change

• X-organs– Neurosecretory tissues in eyestalks– Molt-inhibiting hormone

» Target Y-organ• Y-organs

– Base of maxillae– Releases ecdysone when molt inhibiting hormone is not

present and ecdysis occurs– Androgenic glands (males)

• Promotes development of testes and male characteristics

Page 55: Chapter 14

Class Malacostraca• Excretion– Antennal (green) glands in crayfish– Maxillary glands in others– Homologous to coxal glands of arachnids

• Reproduction– Dioecious– Mating after female molts

• Fertilized eggs attach to female’s pleopods• Others have planktonic larvae

Page 56: Chapter 14

Figure 14.25 (a) Nauplius larva of a barnacle. (b) Zoea larvae of a crab.

(a)

(b)

Page 57: Chapter 14

Order Isopoda• “Pillbugs”• Aquatic and

terrestrial• Dorsoventrally

flattened

Figure 14.26a Order Isopoda.

Page 58: Chapter 14

Order Amphipoda• Laterally

compressed• Crawl or swim

on sides• Beach-hoppers

modified for jumping

Figure 14.26b Order Amphipoda.

Page 59: Chapter 14

Class Branchiopoda• Fairy shrimp

– Temporary ponds• Brine shrimp

– Great Salt Lake• Cladocera

– Freshwater water fleas– Large carapace– Parthenogenesis

common• Flattened, leaflike

appendages

Figure 14.27 Order Cladocera.

Page 60: Chapter 14

Class Maxillopoda• Subclass Copepoda– Most abundant

crustaceans– Important in marine

and freshwater food webs

– First antennae modified for swimming

Figure 14.1 Subclass Copepoda.

Page 61: Chapter 14

Class Maxillopoda• Subclass Thecostracea, Infraclass

Cirripedia– Barnacles–Marine–Monoecious• Nauplius and cypris larvae• Cypris larva settles and metamorphoses into

sessile adult.– Some parasites

Page 62: Chapter 14

Figure 14.28 Class Maxillopoda, Infraclass Cirripedia. (a) Internal structure of an acorn barnacle. (b) A stalked barnacle (Lepas).

Page 63: Chapter 14

Further Phylogenetic Considerations

• Diverse body forms and lifestyles of Arthropoda arose from single ancestor.

• Crustaceans very successful in aquatic habitats

• Chelicerata– First terrestrial arthropods– Account for evolution of many water

conserving features of the phylum• Exoskeletal, excretory, and respiratory

adaptations


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